1. Field of the Invention
The invention relates to a device for measuring surface potentials at a photosensitive body in an electrostatic recording apparatus. More particularly, it is directed to a device for measuring surface potentials at a photosensitive body which corrects surface potential measurement errors caused by eccentricity, noise, and the like to an electrostatic recording apparatus using such surface potential measurement device.
2. Prior Art
As shown in FIG. 4, a conventional circuit for measuring surface potentials at a photosensitive body detects a surface potential at a photosensitive body 1 using a potential sensor 2, measures the surface potential by converting the detected voltage level with a measurement circuit 7, and holds the measured surface potential at a predetermined timing by a sample-hold circuit 5. The control of corona currents at a charging unit 14 is performed by a control circuit 8 based on the measured surface potential. Reference numeral 15 designates a corona power source (see Japanese Patent Unexamined Publication No. 29856/1980).
In the above conventional art, if the potential sensor 2 is of such a type that relative values are outputted, eccentricity of the photosensitive body 1 causes the distance between the photosensitive body 1 and the potential sensor 2 to fluctuate, thereby varying potential sensor outputs. As a result, errors are introduced into measured surface potentials, which further leads to improper controls in subsequent processes, ending up with inconsistent printing quality. Further, independently of the type of potential sensor, these problems are similarly encountered if the potential sensor outputs are contaminated by noise.